all measurements contain a number and a unit. - district 186 1.2.pdf · all measurements contain a...

All measurements contain a number and a unit.

Every unit is based upon standard.

Units and Standards

•  A standard is an exact quantity that people agree to use to compare measurements.

2 Standards of Measurement

Measurement Systems

•  The English system of measurement is commonly used in the United States.

•  Most other nations use the metric system—a system of measurement based on multiples of ten.

Standards of Measurement

2

International System of Units •  All SI standards are universally accepted

and understood by scientists throughout the world.

•  The standard kilogram is kept in Sèvres, France.

Standards of Measurement

•  All kilograms used throughout the world must be exactly the same as the kilogram kept in France.

2

International System of Units

•  Each type of SI measurement has a base unit.

Standards of Measurement

•  The meter is the base unit of length.

2

International System of Units

•  Every type of quantity measured in SI has a symbol for that unit.

Standards of Measurement

•  All other SI units are obtained from these seven units.

2

SI Prefixes

•  The SI system is easy to use because it is based on multiples of ten.

Standards of Measurement

2

SI Prefixes

Standards of Measurement

•  The most frequently used prefixes are shown.

•  Prefixes are used with the names of the units to indicate what multiple of ten should be used with the units.

2

Prefixes 1 kilo (unit) = 1 000 (base)

1 (base) = 1 (base)

10 deci (base) = 1 (base) 100 centi (base) = 1 (base) 1000 milli (base) = 1 (base)

1 000 000 µ (base) = 1 (base) 1 000 000 000 nano (base) = 1 (base)

Measuring Distance •  In scientific measurement length is the

distance between two points.

Standards of Measurement

•  The SI base unit of length is the meter, m.

•  Metric rulers and metersticks are used to measure length.

2

Measuring Volume

•  The amount of space occupied by an object is called its volume.

Standards of Measurement

•  If you want to know the volume of a solid rectangle, such as a brick, you measure its length, width, and, height and multiply the three numbers and their units together (V = 1 x w x h).

2

Measuring Volume

•  For a brick, your measurements probably would be in centimeters.

Standards of Measurement

•  The volume would then be expressed in cubic centimeters, cm3.

2

Measuring Liquid Volume

•  In measuring a liquid’s volume, you are indicating the capacity of the container that holds that amount of liquid.

Standards of Measurement

•  The most common units for expressing liquid volumes are liters and milliliters.

2

Measuring Liquid Volume •  A liter occupies the same volume as a cubic

decimeter, dm3.

Standards of Measurement

•  A cubic decimeter is a cube that is 1 dm, or 10cm, on each side.

2

Measuring Matter

•  Mass is a measurement of the quantity of matter in an object.

Standards of Measurement

•  A bowling ball has a mass of about 5,000 g.

2

Measuring Matter

Standards of Measurement

•  This makes its mass roughly 100 times greater than the mass of a golf ball and 2,000 times greater than a table-tennis ball’s mass.

2

Density •  The mass and volume of an object can be

used to find the density of the material the object is made of.

Standards of Measurement

2

Density

Standards of Measurement

•  Density is the mass per unit volume of a material.

2

Density

Standards of Measurement

•  You find density by dividing an object’s mass by the object’s volume. Density = mass/volume

2

Derived Units

•  The measurement unit for density, g/cm3 is a combination of SI units.

Standards of Measurement

•  A unit obtained by combining different SI units is called a derived unit.

•  An SI unit multiplied by itself also is a derived unit.

2

Measuring Time and Temperature •  It is often necessary to keep track of how

long it takes for something to happen, or whether something heats up or cools down.

Standards of Measurement

•  These measurements involve time and temperature.

•  Time is the interval between two events.

•  The SI unit for time is the second.

2

What’s Hot and What’s Not

•  Think of temperature as a measure of how hot or how cold something is.

Standards of Measurement

•  For most scientific work, temperature is measured on the Celsius (C) scale.

2

What’s Hot and What’s Not

Standards of Measurement

•  On this scale, the freezing point of water is 0°C, and the boiling point of water is 100°C.

•  Between these points, the scale is divided into 100 equal divisions. Each one represents 1°C.

2

Kelvin

Standards of Measurement

•  The SI unit of temperature is the kelvin (K).

•  Zero on the Kelvin scale (0 K) is the coldest possible temperature, also known as absolute zero.

•  Absolute zero is equal to -273°C which is 273° below the freezing point of water.

2

Fahrenheit

Standards of Measurement

•  The temperature measurement you are probably most familiar with is the Fahrenheit scale, which was based roughly on the temperature of the human body, 98.6°.

2

Making Measurements

•  Measured values are reported such that only the last digit is estimated.

•  In other words, when you are recording a measurement, you should write down all of the digits that you are able to read off of the scale on the instrument, plus one additional, estimated digit.

Length Measurements

10 11 12 13 14

What is the measurement?

A) 12.92 m B) 12 m C) 12.9 m

Length Measurements

10 11 12 13 14

What is the measurement?

A) 10.3 m B) 10.28 m C) 10 m

Length Measurements

10 11 12 13 14

What is the measurement?

A) 11.5 m B) 11.55 m C) 11 m

Meniscus

Section Check

A __________ is an exact quantity that people agree to use to compare measurements.

A. variable B. standard C. unit D. control

2 Question 1

Section Check

2 Answer

The answer is B. SI standards are universally accepted and understood by scientists throughout the world.

Section Check

The amount of space occupied by an object is called _________.

2 Question 3

Section Check

The answer is volume. To find the volume of a solid rectangle, measure the rectangle’s length by its width by its height.

Answer 2